1. Field of the Invention
The present invention relates to image processing apparatuses.
2. Description of the Related Art
There are some cases that printouts produced from a single image data item by an output unit provided in an image processing apparatus vary in densities due to a chronological change in characteristics specific to the output unit provided in the image processing apparatus. To reduce such chronological density variation, a technique of causing an image processing apparatus to output a tone-correction-parameter generation sheet has conventionally been employed. In this technique, the tone-correction-parameter generation sheet is read out to calculate a tone correction parameter for use in calibration of tone characteristics of the output unit.
Examples of a technique of reading out a tone-correction-parameter generation sheet by using a high-precision colorimeter or a flatbed scanner are disclosed in Japanese Patent Application Laid-open No. 2005-260305 and Japanese Patent No. 3241986.
In the technique disclosed in Japanese Patent Application Laid-open No. 2005-260305, a scanner profile that specifies a relationship between readout values obtained by a scanner by scanning a readout target placed on a platen and color measurement values of the readout target is created for each of positions on the platen. In this technique, scanner data obtained by scanning a patch printed by a printing unit at any one position of the positions on the platen is corrected by using a scanner profile for the one position. This configuration allows correcting a position-to-position readout error caused by the scanner.
In the technique Japanese Patent Application Laid-open No. 2005-260305, a plurality of standard color sheets is used to create the scanner profiles for each of the positions on the platen. More specifically, in this technique, a method (multiple-sheet method) of creating the scanner profiles by using, as the scan target, a plurality of different color sheets, each of which is a single-color sheet, is employed.
However, the multiple-sheet method is disadvantageous in that color measurements for all of the positions and for all of the plurality of sheets must have been conducted.
Furthermore, when the multiple-sheet method is employed, accuracy of a tone correction parameter may deteriorate by flare phenomenon. The flare phenomenon is a phenomenon that, even when density levels of target points are equal to each other, readout values of the target points obtained by a scanner may vary depending on images around the target points. More specifically, the multiple-sheet method is disadvantageous in that, in a situation where a layout of a sheet for use in creating scanner profiles differs from a layout of a sheet for use in creating tone correction parameters, as a result an accuracy of the generated tone correction parameter may deteriorate.
To prevent the deterioration in accuracy of the tone correction parameter caused by the flare phenomenon, the above-described two types of sheets are desirably identical in layout. However, the multiple-sheet method requires a plurality of sheets to be printed not only when creating scanner profiles but also when creating a tone correction parameter, and therefore a huge man-hour is required.